Is this a bug? There are some servers that won't show up unless I disable all other ports.

For example: I have to disable odamex and zdaemon and refresh the list many times to see all zandronum servers. I noticed that because there are some servers that I play that won't be listed the first time I get the list from the master.

no. its probably problem with your computer settings: operating system, programs or ide.. or may be hardware (wifi?) try to manipulate ide's refresh speed: set it to normal, or custom with large value of SendDelay parameter btw what are "some servers"? always the same set? or different?

t3h unnamed, boss battles, beast incantation. I play these quite often and began to notice that sometimes they were missing from the list (doing a search for t3h, boss battles or beast, returned no results or different servers from the ones I know).